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questions regarding bandwidth statement

Unanswered Question
Oct 21st, 2006
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We use IPsec tunnels to connect to all the remote sites. We just upgraded our bandwidth from 512 K to full T1 of the remote sites. We did not change any bandwidth statement on the interfaces, but all the users are experiencing better performance. Does that bandwidth statement matter? Also from the netflow analyzier, it only shows 8k of the IPsec tunnel. I know it is T1 bandwidth now; should I change the bandwidth statement to full T1?

thanks for the help,


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Adam Frederick Sat, 10/21/2006 - 17:47
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I think it is best practice to specify the bandwidth statement. Especially if you are using routing protocols, especially OSPF in particular. You are seeing 8k as your tunnel bw because this is the default for tunnel interfaces. Please note if the interfaces do not have any bandwidth statement what so ever, it will default to the interface default (serial=1.544 in USA). Below is output from a 3725


c3745#show interfaces tunnel 0

Tunnel0 is up, line protocol is up

Hardware is Tunnel

Internet address is

MTU 1514 bytes, BW 9 Kbit, DLY 500000 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation TUNNEL, loopback not set

Keepalive not set

Tunnel source, destination

Tunnel protocol/transport IPSEC/IP

Tunnel TTL 255

Fast tunneling enabled

Tunnel transmit bandwidth 8000 (kbps)

Tunnel receive bandwidth 8000 (kbps)

royalblues Sat, 10/21/2006 - 18:14
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As stated earlier Bandwidth statement is necessary when you run routing protocols like EIGRP & OSPF which calculate their metric based on the bandwidth statement.

It will not affect the performance if you do not change the bandwidth statement but if you are using any NMS tool for monitoring then they may report the utilization and other statisitcs based on it.



Richard Burts Sun, 10/22/2006 - 11:12
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Gene asked if the bandwidth statement matters and about the bandwidth reported for his tunnel. Adam responded correctly that every interface has a default bandwidth and that for tunnels it is 9K. He also points indirectly to the use of bandwidth in the calculation of metric by OSPF and EIGRP. Narayn's response is more explicit about the use of bandwidth to calculate the metric in EIGRP and OSPF and he correctly points out that management software typically uses the interface bandwidth in calculating interface usage. And with in inaccurate bandwidth on the inteface the performance reporting will be inaccurate.

In addition I would point out that EIGRP by default will use no more than 50% of the interface bandwidth for sending of EIGRP protocol traffic. Using the default bandwidth on the tunnel interface could result in some problems for EIGRP (if EIGRP were running over the tunnel).




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